1. Field of the Invention
The present invention relates to a write head with a multi-stitched second pole piece and more particularly to a write head wherein the second pole piece has a second layer component that is stitched (magnetically connected by engagement) to top, back and first and second side edges of a first layer component.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly mounted on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent the ABS to cause the slider to ride on an air bearing a slight distance from the surface of the rotating disk. The write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted through the coil layer induces a magnetic field across the gap between the pole pieces. This field fringes across the gap at the ABS for the purpose of writing information in tracks on moving media, such as in circular tracks on a rotating disk.
The second pole piece layer has a pole tip portion which extends from the ABS to a flare point and a yoke portion which extends from the flare point to the back gap. The flare point is where the second pole piece first begins to widen (flare) after the ABS to form the yoke. The placement of the flare point directly affects the magnitude of the write field at the recording medium. Since the magnetic flux decays as it travels down the length of the second pole tip, more flux will reach the recording media if the length of the second pole tip is made short. Therefore, optimal performance can be achieved by aggressively placing the flare point close to the ABS so that the second pole tip is short.
Another parameter important in the design of the write head is the location of the zero throat height (ZTH). Zero throat height is the location where the first and second pole pieces first separate from one another after the ABS. The ZTH separation is caused by the contour of an insulation layer, typically the first insulation layer in the insulation stack. Flux leakage between the first and second pole pieces is minimized by locating the ZTH as close as possible to the ABS.
Unfortunately, the aforementioned design parameters present a dilemma in the fabrication of the second pole tip. The second pole tip should be well-defined in order to produce well-defined written tracks on the rotating disk. Poor definition of the second pole tip may result in overwriting of adjacent tracks. A well-defined second pole tip should have parallel planar side walls which are perpendicular to the horizontal plane of the first pole piece layer. In many prior art write heads the second pole tip is formed along with the yoke after the formation of the first insulation layer, the coil layer and the second and third insulation layers of the insulation stack. Each insulation layer includes a hard-baked photoresist having a sloping front surface.
The sloping surface of each insulation layer has an apex angle with respect to a plane normal to the ABS. After construction, the first, second and third insulation layers present sloping surfaces which face the ABS. The sloping surfaces of the hard-baked resist exhibit a high optical reflectivity when they are coated with a seedlayer for the purpose of frame plating the second pole piece layer. When the second pole tip and yoke are constructed, a thick layer of photoresist is spun on top of the coated insulation layers and photo patterned to shape the second pole tip, using a conventional photo-lithography technique. In the photo-lithography step, light is directed vertically through slits in an opaque mask, exposing areas of the photoresist which are to be removed by a subsequent development step. One of the areas to be removed is the area where the second pole piece (pole tip and yoke) are to be formed by plating. Unfortunately, when the location of the flare point is placed on the sloping surfaces of the insulation layers light is reflected forward toward the ABS into photoresist areas at the sides of the second pole tip area. After developing, the side walls of the photoresist are notched which causes the pole tip to be poorly formed after plating. This is called xe2x80x9creflective notchingxe2x80x9d which causes overwriting of adjacent tracks on a rotating disk. It should be evident that, if the flare point is recessed far enough into the head, the effect of reflective notching would be reduced or eliminated since it would occur behind the sloping surfaces. However, this solution produces a long second pole tip which quickly degrades the head""s ability to effectively write on the recording medium.
In order to overcome the aforementioned reflective notching problem some second pole pieces are constructed from two or more layer components wherein a front layer component forms the second pole tip and a back layer component forms a yoke portion of the second pole piece. The second pole tip component may be constructed after a zero throat height (ZTH) defining insulation layer, but before other insulation layers to eliminate the reflective notching problem. After forming the write gap layer and the ZTH defining insulation layer, a photoresist layer is spun on the partially completed head. The photoresist layer is mostly flat so that light from the photo-patterning step is not reflected forward into a pole tip region. The second pole tip component is then frame plated into a well formed opening in the photoresist layer and then the photoresist layer is removed. The sequence of construction is then the first insulation layer, the coil layer and the second and third insulation layers. The second pole yoke component is then frame plated causing it to be stitched to the top surface of the second pole tip component. The write head formed by this process is referred to as a stitched write head.
While the stitched write head overcomes the reflective notching problem it presents additional problems. The top surface of the second pole tip component is required to have sufficient area for stitching it to the second pole yoke component. Prior art stitching schemes cause additional flux to be leaked between the second pole tip component and the first pole piece layer since the second pole tip component is closer to the first pole piece layer over a greater area. Prior art stitching also requires the one or more coil layers to be located further back in the head which increases the reluctance of the write head circuit which, in turn, increases the rise time and decreases the data rate of the signal. Further, when the second pole tip component extends to the ABS the second pole tip component and the first pole piece layer form a T configuration. During operation of the head flux fringes from the cross of the T to the upright portion of the T which causes overwriting of adjacent tracks.
The present invention provides a unique stitching scheme wherein the stitched area at the top surface of the second pole tip component is reduced. This is accomplished by stitching the second pole yoke component to a much smaller top surface of the second pole tip component as well as to a back edge and first and second side edges of the second pole tip component. The extra stitching at the back edge and the first and second side edges of the second pole tip and yoke component provides the required magnetic coupling between the second pole tip and yoke components to transfer flux therebetween. This arrangement shortens the length of the top stitched area so that one or more coil layers can be located closer to the ABS for increasing the data rate of the head. Further, this arrangement reduces the amount of material of the second pole piece layer in close proximity to the first pole piece layer so as to minimize flux leakage therebetween.
In a preferred embodiment of the invention a ZTH defining layer, other than one of the aforementioned insulation layers, separates the second pole tip component from the first pole piece layer so as to further minimize flux leakage between the pole pieces. The flare point of the second pole tip component is preferably located on a flat portion of the ZTH defining layer so as to prevent reflective notching. In another preferred embodiment one of the insulation layers of the insulation stack is spaced from the back and first and second side edges of the second pole tip component so as to form a U shaped trench in which a front portion of the second pole yoke component is located. The invention is easily adapted to single or multiple coil layers, an inset ZTH defining layer and sunken first pole piece types of write heads. It is also preferred that the second pole tip component be recessed from the ABS so as to minimize flux leakage between the pole tips at the ABS.
An object of the present invention is to provide a stitched write head wherein one or more coil layers can be moved closer to the ABS so as to minimize reluctance and increase the data rate of the write head circuit.
Another object is to provide a stitched write head wherein flux leakage between the first and second pole pieces is reduced.
A further object is to provide a more efficient write head wherein reflective notching has been obviated, the data rate has been increased and flux leakage between the first and second pole pieces has been reduced.
Other objects and advantages of the invention will become apparent upon reading the following description taken together with the accompanying drawings.